Process for electrooptical reg



Aug. 22, 1933. 1,923,619

A. GUERBILSKY PROCESS FOR THE ELECTROOPTICAL REGISTERING OE SOUNDS ORANY 0TH ELASTIC WAVES led May 1951 QJTWMWAA/V/Z/W Patented Aug. 22,-1933 PATENT OFFICE ELECTROOPTICAL REG- PROCESS" FOR ISTER OF SOUNDS ORANY OTHER ELASTIC WARES 7 Alexis Guerbilsky, Paris, France ApplicationMay 23,1931, Serial No. 539,606, and

in France May 24, 1930 4 Claims. (Cl. 179-1003) My invention relates toprocesses for the electro-optical registering of sounds or 'any otherelastic waves, which are based on the use of piez'o-electric crystalsfor modulating luminous waves in accordance with the sounds or otherwaves to be recorded. 2

These processes involve the use of an oscillatory circuit and of apiezo-electric crystal having both exactly the same frequency, so thatthe luminous variations which can be recorded by the known methods. Upto this time it has been found impossible for practical 'purposetoobtain a satisfactory result through processes of that kind, due to theacuity 'of resonance of the piezo-electric crystals. Very slightaccidental variations 'of the frequency of-the oscillatory circuit or ofthe frequency of "ther'crystals are sufficient for destroying tuning.Furthermore, said acuity of resonance of the crystals is accompanied byasmall logarithmic decrement of their oscillations which rendersmodulation very difficult unless special'precautions are taken. Thus,for example, some authors have recommended an arti- 330 ficial dampingof the oscillations of the crystals.

, 5 these disadvantages by. making use, for the recording of. elasticwaves, of fpiezo electric resonators adapted to vibrate in tune not withone single-frequency, but with 'several frequencies,

forinstancewith'a wholerange of frequencies. My invention also includesseveral particular arrangements making it possible to effect, forpractical purposes, in a-simple and efficient manner, theiegistering' ofelastic waves in accordance with'theprinciple of my invention.

My: invention m'akesit possible to register elasticwaves, and, inparticular, sounds,':as well by the method of inscription=calledvariable density method which consists in causingthe luminous intensityof a light beam of fixed di-- .50v rection to .vary as by the so.called"variable ordinates method which consists in'va'r'ying thedirection of a light beam of fixed intensity.

In the first case (variable density method), I actupon thepiezo-electric resonators by means of an alternating electrostatic fieldhaving the same frequency as the resonators or a harmonic of saidresonators, and I cause that field to be modulated in accordance withthe amplitude of the elastic vibration to .be registered. In that case,I obviate the disadvantage result- '60 ing from the acuity of resonanceby making use 1 of resonators corresponding to different frequencies.

The method of utilizing the vibrations of the resonators for theproduction of optical effects may be of any suitable type. J Thus in myU. S. patent application Ser. No. 272,319 filed Apr. 23, 1928, and inmyFrench patent filed Sept. 21, 1929, I have disclosed several suchmethods. In particular I may make use of a prism of quartz whosefrequencyvaries from one point to another according to its thickness. Bysuitably choosing the angle. of the prism, it is possible to obtain,according to the case, luminous "spots of. different dimensions. ,75Besides, .said angle may be chosen very small 1 and the prism maydiflFer but by part of the thickness of a fringe from a plate havingparallel faces as the one referred to by some authors but whichdid notgive satisfactory results. It should be noticed that in this case as inthe case of a group of quartz described in'my above mentioned patents,the localized resonances must not necessarily be utilized with polarizedlight. It is quitepossible to make use of the Giebe and Scheibe'efiector of any other known phenomenon. 7 'It is also possible, instead of,modulating the intensity of the field to modify its frequency, which hasfor its result to produce a displace- .9 ment of the luminous spot; Itis possible to soadjust said displacements with respect to an openingsuch as a slot that they cause variations of" the intensity of the lightbeam issuing from said aperturethat are proportional to the 5 frequencyof the field." Nowit is possible to cause said frequency to depend onthe elastic condenser from which depends the frequency. of I the field;The displacements of said membrane 1 can cause the capacity of thecondenser to vary, 10'5 either as a result of the variation in the dis-'tance between the armatures, or owning 110413119 variation of pressureof a gas that would constitute the dielectric of the, condenser. It isalso possible to useto this effect a microphone 1 10'.

and to cause the microphonic current to act upon the frequency of theabove mentioned field through any known method. However it is evidentlypreferable to avoid the microphone and to use a variable capacitycondenser which does not necessitate any amplifying arrangement.

In the second case (variable ordinates meth- 0d) the device for carryingout the process will be the same but the displacements of the luminousspot will be directly utilized.

Inthe case of feeble energies to be registered or of variable condensersthat are not very sensitive I may amplify the relative variations of thefrequency that act upon the resonators by the following method:

I produce by means of the condenser variations of a very high frequency;said variations are caused to produce beats with a fixed frequency, andc is the difference of the two frequencies which is caused to act on thetwo resonators. In that way, the absolute variations of the frequencydetermined directly by the condenser and of the frequency acting on theresonators are the same, but the relative variations are greater for thelast mentioned frequency, since it is smaller.

It should be well understood that in the preceding specification, aswell as in what follows, the term piezo-electric resonator is intendedto designate not only piezo-electric crystals, but also combinations ofsaid crystals with other bodies, and even substances that are rendered,through any suitable process, capable of vibrating in resonance underthe action of an alternating electrostatic field. It is further possibleto replace the piezo-electric resonators by other resonators, forinstance by resonators capable of vibrating under the action of anelectro-magnetic field which would replace, in that case, theelectro-static field. It is also possible to make use ofmagneto-striction. In order to utilize, in that latter case the actionof the vibrating rods, several processes may be chosen, such asinterference fringes, which, of course may be also made use of in thecase of piezoelectric crystals.

Preferred embodiments of my invention will be hereinafter described withreference to the appended drawing, given merely by way of ex ample, andin which: 7

Fig. 1 is a diagrammatical view of an oscillatory circuit provided withthe piezo-electric resonator;

Fig. 2 is a diagrammatical view of the optical system;

Figs. 3a. and 3b are curves adapted to illustrate the operation of thesystem; and

Figs. 4 and 5 are detail views.

In Fig. 1, I have shown a standard arrangement of oscillatory circuitwhose frequency is determined by coil L and the capacity of variablecondenser C as above explained.

I have shown in Q a prism of quartz placed between two armatures 1 and2, connected to the terminals of a coil L coupled with coil L.

In Fig. 2 I have shown the optical arrangement. The source of light S isplaced at the focus of a lens Z. The parallel beam passes through apolarizer P and an analyzer A in the extinction position. Between P andA is placed the prism of quartz Q, and in order to reestablishextinction, a compensator Q. Compensator Q consists, for instance of aplate of quartz having the same thickness as Q, but rotated through anangle of with respect to Q. The system is completed by a lens L formingan image of Q on the sensitized film f disposed behind a slot a.

When condenser C is not subjected to any pressure, prism Q is notenergized, the frequency of the current being outside of the range offrequencies for which it resonates. On the contrary, when a pressure,due for instance to acoustic vibrations (human voice, noises to beregistered and the like) acts upon condenser C, its capacity varies andtogether with it the frequency of the electric oscillations. A part ofthe prisms then breaks into oscillations, and its image, formed on thefilm, is lighted in such manner that the film is recorded.

If the angle of the prism is very small, the luminous part will extendalong a relatively great length and the variations of the frequency willproduce displacements of the luminous spot along the spot, the spotscorresponding to the various frequencies overlapping each other, so thattheir succession in time will be recorded on the film by a white sideand a black side, 7 the line of separation being a sinuous curvecorrespondingto the displacements of the spot, and therefore to thefrequency of the electric circuit, which itself depends on the pressureexerted on the condenser. M

Figs. 4 and 5 show examples of piezo-electric resonators. In Fig. 4, theresonator comprises a single crystal whose faces 3 and 4 make a smallangle. In Fig. 5 the resonator consists of a plurality of crystals ofdecreasing length,- The planes passing through the angles 5 and no 6 ofthe crystals also make in this embodiment a very small angle. Said angleshould preferably be so small that the breadth of the part of theresonator that is set in vibration for-- a given frequency may begreater than the amplitude of the displacement of said part under theaction of the variations of frequency to be registered.

In Fig. 3 I have shown two curves a and b.- Curve 0. shows, for example,the quantity of light as a function of the frequency when the prism isreplaced by a plate having parallel faces.

Curve b indicates the same relation for prism s Q. The ordinates areproportional to the quantity of light of the image of any part of theprism.

The essential difference between these two cases will be easily shown bythese twofiguressj' It should be well understood that my invention isnot limited to the above described embodiments, but that changes may bemade therein without departing from the principle of my invention ascomprehended within the scope" of the appended claims.

What I claim is:

1.'A device for the electro-optical registering of elastic waves, and inparticular of sounds which comprises, an electric circuit, a source ofhigh frequency current in said circuit, means for varying the intensityof the current in said circuit that are sensitive to the action of saidelastic waves, a piezo-electric crystal of nonuniform thickness in thedirection of its electric axis coupled with said circuit, and opticalmeans adapted to cooperate with said crystal.

'2. A device for the electro-optical registering of elastic waves, andin particular of sounds, which comprises in combination, an electriccircuit, a source of high frequency current in said circuit, means,sensitive to the action of said elastic waves, for varying the intensityof the current in said circuit, a piezo-electric crystal having twoopposite faces making an angle with each other disposed in said circuitso that said faces of said crystal are those across which extends itselectric axis, and optical means adapted to cooperate wtih said crystal.1

3. A device for the electro-optical registering of elastic waves, and inparticular of sounds, which comprises in combination, an electriccircuit, a source of high frequency current in said circuit, meanssensitive to the action of said elastic waves for varying the intensityof the current in said circuit, a prism of quartz having two oppositefaces that make a small angle with each other coupled with said circuitsothat the said faces of the prism of quartz are those across which itselectric axis extends, and optical means adapted to cooperate with saidprism of quartz.

' 4. A device for the electro-optical registering of elastic waves, andin particular of sounds, which comprises in combination, an electriccircuit, a source of high frequency current in said circuit, meanssensitive to the action of said elastic waves for varying the intensityof the current in said circuit, a piezo-electric resonator consisting ofa series 'of piezo-electric crystals having substantially parallelopposite faces disposed in adjacent relation with one another, the edgesof said crystals being substantially located in two planes making asmall angle with each other, said piezo-electric resonator being coupledto said electric circuit in such manner that said faces of the crystalsare parallel to the field in which the resonator is placed, and opticalmeans adapted to cooperate with said resonator.

ALEXIS GUERBILSKY.

